1. Technical Field
The disclosure relates to an image processing device, an image processing method, a microscope system, and a computer-readable recording medium for performing shading correction on images acquired by imaging specimens or the like.
2. Related Art
In recent years, the so-called virtual slide technology that registers an image taken of a specimen placed on a slide glass as electronic data so that a user can observe the image on a monitor of a personal computer or the like has been known. The virtual slide technology sequentially joins partial images of a specimen enlarged by a microscope together, thereby constructing a high-resolution image of the entire specimen. Specifically, a technology of acquiring a plurality of images of different fields of view on the same subject, and joining these images together to generate an enlarged image of the subject is the virtual slide technology.
Microscopes consist mainly of a light source to illuminate a specimen and an optical system to enlarge an image of the specimen. At a later stage of the optical system, an imaging element to convert an enlarged image of a specimen into electronic data is provided. Therefore, there is a problem that unevenness in brightness is produced in an acquired image due to unevenness in illuminance of the light source, nonuniformity of the optical system, and in addition, unevenness in the characteristics of the imaging element, and the like. The unevenness in brightness is called shading, in which the brightness generally changes to be darker as it moves away from the center of an image corresponding to the location of the optical axis of the optical system. Therefore, when a plurality of images is joined together to create a virtual slide image, unnatural boundaries are produced at the joints of the images. Further, by joining a plurality of images, shading is repeated. Thus it seems as if there is a periodic pattern on the specimen.
To counter this situation, a shading correction technology of acquiring a shading pattern previously as a calibration image, and correcting an image of a specimen, based on the calibration image is known. For example, Japanese Laid-open Patent Publication No. 2006-171213 discloses a shading correction technology of using, as a calibration image, an image acquired by performing, for transmitted-light illumination observation, imaging with a specimen retracted outside the angle of view of an optical system, or performing, for epi-illumination observation, imaging with a reflective member disposed in the angle of view of the optical system. Japanese Laid-open Patent Publication No. 2008-51773 discloses a method of acquiring data for shading correction by performing imaging with a uniform fluorescent sample as a calibration sample for fluorescent observation.